Sigmoid notch implant

ABSTRACT

A sigmoid notch resurfacing prosthesis for application to the sigmoid notch of the distal radius. The sigmoid notch prosthesis generally includes a saddle and a radius portion for attachment to the distal radius. The saddle may be formed from ultra high molecular weight polyethylene or another durable self-lubricating material. The saddle includes an at least partially concave contoured depression having rounded edges that is securable to the radius portion. The saddle may be secured by a sliding notch snap fit design. The prosthesis may be adapted for articulation with the natural head of the ulnar or with an ulnar head prosthesis that has replaced the ulnar head.

STATEMENT OF RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/001,572, filed on Dec. 1, 2004 (allowed), which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention pertains generally to orthopedic prostheses. Moreparticularly, the present invention pertains to a joint prosthesis forthe distal radioulnar joint.

BACKGROUND OF THE INVENTION

The radius and ulna together form the bony structure of the forearm. Thetwo bones articulate with one another at both their proximal and distalends. The distal radioulnar joint is a “shallow socket” ball joint. Theulna, a relatively straight bone, translates dorsal-palmarly to acceptthe modestly bowed radius. The distal end of the radius articulates inpronation and supination on the distal head of the ulna at the sigmoidnotch or fossa. The sigmoid notch socket in most wrists is relativelyflat and a number of ligaments support the distal ulna where it meetsthe distal end of the radius. The supporting ligaments include thetriangular fibrocartilage (TFC), the extensor carpi ulnaris (ECU)subsheath, and the ulnar collateral ligament complex. The stabilizingelements of the triangular fibrocartilage, the extensor carpi ulnarissubsheath, and the ulnar collateral complex work in cooperation with thedistal ulna to transfer compressive loads between the ulnar carpus andthe distal ulna across the distal radioulnar joint.

Unfortunately, fractures of the distal radius and other injuries of theforearm commonly occur and may cause rotational instability. Followingthese injuries to the forearm, ligament disruption, ulnar styloidfractures, and fractures into the distal radioulnar joint commonlyoccur. Fracture or dislocation involving the distal radioulnar jointoften results in a loss of forearm rotation related to eitherinstability or incongruity between the sigmoid fossa of the distalradius and the head of the ulna. A variety of different fracturesinvolving the distal radius can cause this condition including theColles' fracture and the Galeazzi fractures.

When there is loss of stability of the distal radioulnar joint,subsequent weakness in grip and pinch as well as potential loss offorearm rotation occur. Instability can also be associated with aninjury to the triangular fibrocartilage or to the ulnar styloid. Wheninstability is present, a number of ligament reconstructive procedureshave been devised to assist in treating the unstable distal ulna.Unfortunately, ligament reconstruction of the distal ulna often does notrestore complete stability and joint replacement is often performed inan effort to stabilize the joint.

Sometimes, when the distal ulna is damaged, the preferred treatment ishemiarthroplasty. That is to resect the head of the ulna and replace itwith an ulnar head prosthesis which then is in contact with the naturalbone of the radius. The prosthesis then articulates with the sigmoidnotch to restore functionality to the distal radioulnar joint.Unfortunately, long term articulation between the man made implant andthe natural bone may accelerate wear of the bone and lead to arthriticor degenerative change. This may cause the patient pain and restrictionof motion.

In other circumstances, both the head of the ulna and the distal radiusmay suffer injury, arthritic change or degenerative changesimultaneously. Then, it would be desirable to replace the articularsurfaces of both the head of the uina and the sigmoid fossa. Inaddition, in some cases, replacement of the ulnar head with a prosthesisdoes not fully restore stability to the distal radioulnar joint. Atpresent, patients that have had an ulnar head resection withimplantation of an ulnar head prosthesis who still suffer frominstability have few options.

In light of the foregoing, the surgical arts would benefit from accessto a prosthetic device that could be used to restore the function of adamaged sigmoid notch articular surface. The surgical arts would alsobenefit from the availability of a prosthetic combination to repair aninjured or degenerated distal radioulnar joint.

SUMMARY OF THE INVENTION

The invention solves many of the above referenced problems. Theinvention includes a sigmoid notch resurfacing prosthesis forapplication to the sigmoid notch of the distal radius. The sigmoid notchprosthesis generally includes a saddle and a radius portion forattachment to the distal radius. The saddle is securable to the radiusportion and includes an articular surface having an at least partiallyconcave contoured depression having rounded edges. The saddle may besecured by a sliding notch snap fit design or by other techniques knownto those skilled in the art. The saddle may be formed from ultra highmolecular weight polyethylene or another durable self-lubricatingmaterial for articulation with the head of an ulnar head implant. Atthis time, it is thought that metallic materials such as stainless steelor titanium are preferable for articulation with natural bone if thesigmoid notch implant is used as a hemiarthroplasty.

The invention may also include an ulnar head prosthesis for replacingthe distal head of the ulna. The ulnar head prosthesis includes a headand a stem to replace the distal ulnar head. The prosthesis head isformed with a curved surface for articulation with the sigmoid notchprosthesis when installed. The head presents a bore to allow forattachment of the head to the stem. The head may be formed with sutureholes for anchoring the head to soft tissues that are exposed afterresection of the distal ulna.

The stem of the ulnar head prosthesis is elongated with an extended endfor engaging within the intramedullary canal of the resected ulna. Thestem of the ulnar head prosthesis also includes a distal end adapted forengagement with the bore in the head of the ulnar prosthesis. The stemfurther includes a collar between the proximal end of the stem and thedistal end of the stem. The collar may be substantially flat. Theproximal surface of the collar rests against the resected end of thedistal ulna upon implantation to prevent the stem from penetratingexcessively into the intramedullary canal of the ulna.

The saddle plate of the sigmoid notch implant includes a stem extendingoutwardly from a reverse side thereof as well as a countersunk screwreceptacle for receiving a low profile spherical head bone screw.Interconnecting the screw receptacle and the stem is a stiffening rib.The opposite surface of the radius portion includes a substantially flatplatform and a saddle retainer that surrounds the saddle on three sidesand is grooved to receive a portion of the saddle thereunder to hold thesaddle in place. In addition, the saddle retainer includes a retainingridge so that the saddle can be slid onto the retaining structure andretained by a snap fit. The saddle and the saddle plate can also beconnectable in other way known to those skilled in the art.

The sigmoid notch implant is implanted by first surgically accessing thedistal radial ulnar joint. Once a surgeon decides the precise locationfor the sigmoid notch implant, the surgeon prepares the distal radius bydrilling a hole to accept the stem of the saddle plate. A trial stem isplaced in the hole in order to determine the proper location for pilothole for a self-tapping bone screw. The trial stem has an undersizedstem in order to preserve a press fit between the final implant and thebone of the distal radius.

Once the location of the pilot hole for the self-tapping bone screw iscompleted the surgeon burrs down the sigmoid notch to provide a flatbuttress for the back of the saddle plate. The surgeon also burrs asmall countersink to accept a collar surrounding the head of thespherical screw and the stiffening rib between the screw hole and thestem. The radius portion is then placed into the drill hole and impactedto seat it at its final location. Once the radius implant issuccessfully located, the self-tapping bone screw is placed in the pilothole and tightened. Once the radius plate is fully seated, the head ofthe ulnar head implant is returned to its proper location at the head ofthe ulna.

In this embodiment, the saddle is inserted into the retaining structureof the radius plate and advance distally. Assuming the saddle isproperly aligned with the radius plate, the saddle will move distallyuntil it is about seventy five percent engaged, at which point it willrise up on a ramp in the bottom of the saddle as the ramp passes overthe interference ridge on the surface of the radius plate. Once thesaddle is completely seated in the saddle plate the surgeon reduces thejoint and assesses range of motion. Assuming that relative motion of theulnar head implant and the sigmoid notch implant is satisfactory, thesurgeon repairs the joint capsule and closes the incision and theprocedure is complete.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sigmoid notch implant in accordancewith the present invention;

FIG. 2 is another perspective view of the sigmoid notch implant;

FIG. 3 is a front elevational view of the sigmoid notch implant;

FIG. 4 is a plan view of the sigmoid notch implant;

FIG. 5 is a rear elevational view of the sigmoid notch implant;

FIG. 6 is a side elevational view of the sigmoid notch implant;

FIG. 7 is a perspective view of a saddle in accordance with the presentinvention;

FIG. 8 is a front elevational view of the saddle in accordance with thepresent invention;

FIG. 9 is a perspective view of the saddle in accordance with thepresent invention;

FIG. 10 is a plan view of the saddle with phantom lines showing internalstructures;

FIG. 11 is a rear elevational view of the saddle;

FIG. 12 is a side elevational view of the saddle with phantom linesdepicting internal structures;

FIG. 13 is a plan view of a radius component of the sigmoid notchimplant;

FIG. 14 is a front elevational view of the radius component;

FIG. 15 is a side elevational view of the radius component;

FIG. 16 is a rear elevational view of the radius component;

FIG. 17 is a perspective view of the radius component;

FIG. 18 is another perspective view of the radius component;

FIG. 19 is an elevational view of the sigmoid notch implant and an ulnarhead implant with the saddle of the sigmoid notch implant partiallyinstalled; and

FIG. 20 is an elevational view of the sigmoid notch implant and an ulnarhead implant with the saddle completely installed.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the sigmoid notch implant 30 generally includes radiusportion 32, saddle 34 and bone screw 36: Referring to FIGS. 18 and 19the sigmoid notch implant 30 is generally utilized along with an ulnarhead implant 38. A typical ulnar head implant 38 includes a head portion40 and a stem portion 42. One exemplary ulnar head prosthesis isdisclosed in U.S. Pat. No. 6,302,915. The contents of that U.S. Patentare incorporated herein by reference.

Referring to FIGS. 1-6 and 13-18, radius portion 32 generally includesstem 44 and saddle plate 46. Stem 44 may extend outwardly from saddleplate 46 at a substantially right angle.

Stem 44 includes cylindrical portion 48 and rounded end 50. Stem 44joins saddle plate 46 at fillet 52. Stem 44 may also have a taperedshape or include ridges or surface texturing thereon.

Referring to FIGS. 13-18 saddle plate 46 is roughly trapezoidally shapedand may be integrally formed with stem 44. Saddle plate 46 presentssaddle retainer 54 and retainer ridge 56 on a side opposite from stem44. Saddle plate 46 also defines screw hole 58 there through.

In one embodiment, saddle retainer 54 is structured to substantiallysurround saddle 34 on three sides. Saddle retainer 54 includes ridge 60on three sides thereof, which together define a three-sided groove 62.Surface 64 of saddle plate 46 is substantially planar. Retaining ridge56 extends upwardly from surface 64 at an end of saddle plate 46substantially opposite from saddle retainer 54. Retaining ridge 56 mayhave a bevel 66 on the top thereof.

Screw hole 58 passes through saddle plate 46. Screw hole 58 desirablyincludes spherical countersink 68. As seen in FIGS. 14-16 and FIG. 18,screw hole 58 also passes through collar 70 which may be integrallyformed with saddle plate 46 and which joins saddle plate 46 at circularfillet 74. Collar 70 is connected to stem 44 by stiffening rib 76 whichinterconnects circular fillet 74 with fillet 52. Stiffening rib 76 mayalso be integrally formed with saddle plate 46. Screw hole 58 may belocated beneath saddle 34 when saddle 34 is assembled to saddle plate 46or screw hole 58 may be in a location left exposed when saddle 34 isassembled to saddle plate 58.

Screw hole 58 defines cylindrical portion 78 on its inner aspect.Spherical countersink 68 defines circular bevel 80 where it meetssurface 64.

Radius portion 32 is desirably machined, cast, molded or otherwiseformed from a single piece of material. Radius portion 32 may bemanufactured from implant grade 316L stainless steel or otherbiocompatible materials such as titanium. Biocompatible polymer orcomposite materials may be used as well.

Radius portion 32 may be mirror polished over surface 64, saddleretainer 54 and retaining ridge 56 and any other surfaces that do notmake direct contact with the bone of the radius. The surfaces of stem44, collar 70, stiffening rib 76, fillet 52 and circular fillet 74 andany other surface that makes contact with the bone of the radius may beroughened to encourage osseointegration such as by the application ofcommercially pure titanium plasma coating.

Saddle 34 presents articular portion 82 and securing portion 84.Referring to FIGS. 8-12, articular portion 82 presents articular face 85which includes concave portion 86 and convex portion 88. Concave portion86 and convex portion 88 are contoured so that articular face 85substantially conforms to the shape of an ulnar head implant 38.Articular portion 82, desirably, has a radiused edge 90. Perimeter 92 ofsaddle 34 substantially conforms to the shape of the perimeter of saddleplate 46. The outline of saddle 34 is generally trapezoidal and includesrounded comers 94.

In an exemplary embodiment, concave portion 86 may be substantiallyspherical and have a radius of curvature of about 0.709 inches. Convexportion 88 may have a radius of curvature of about 0.5 inches. Thesevalues are exemplary and should not be considered limiting. Adjacent toconvex portion 88 is sloped portion 96 which maybe sloped at aboutseventy degrees relative to the perimeter 92 of saddle 34. Saddle 34 canbe adjusted in size, thickness and shape to conform to the natural headof the radius or to various ulnar head implants 38.

Securing portion 84 of saddle 34 presents bottom face 98 surrounded bytongue 100. Tongue 100 along with perimeter 92 define groove 102. Groove102 extends substantially around perimeter 92 and is sized andstructured to receive ridge 60 while tongue 100 fits into groove 62.Tongue 100 partially surrounds the edge of bottom face 98 on threesides. Tongue 100 extends outwardly from bottom face 98 and definesadjacent groove 102 which also extends around three sides of bottom face98. Tongue 100 and groove 102 are dimensioned to mate with ridge 60 andgroove 62 of saddle retainer 54.

Bottom face 98 is substantially planar and further presents recess 104.Recess 104 may be substantially rectangular in shape and includes flatportion 106 and sloped portion 108. Adjacent to recess 104 and beyondthe edge of sloped portion 108 is retaining slot 110. Recess 104 isdimensioned so that flat portion 106 can receive retaining ridge 56therein when tongue 100 and groove 102 are aligned with ridge 60 andgroove 62 and saddle 34 is slidably engaged with saddle retainer 54.Retaining slot 110 is dimensioned to receive retaining ridge 56 thereinwhen saddle 34 is slidably secured to radius portion 32. Note thatsaddle plate 46 and/or saddle 34 resiliently flex to make the engagementbetween retaining slot 110 and retaining ridge 56

Saddle 34 may be formed from ultra high molecular weight polyethylene oranother self-lubricating material. Saddle 34 may also be from otherpolymers, composite or metallic material. It is generally believed thatbiocompatible metallic materials are preferred for articulation with thenatural head of the ulna if the sigmoid notch implant 30 is used forhemiarthroplasty. It is specifically contemplated that saddle 34 may bejoined to radius portion 32 by many other techniques as understood bythose of ordinary skill in the art such as the use of screws, clamps orinterference fit techniques.

Bone screw 36 is a spherical head bone screw. Bone screw 36 includesspherical head 112 and shaft 114. Shaft includes threaded portion 116and unthreaded portion 118. Bone screw 36 desirably includes flutes 20to facilitate a self-threading design. Bone screw 36 may be manufacturedto the standards of ISO 5835. Referring to FIG. 5, bone screw 36 mayangulate in a conical fashion at an angle alpha within sphericalcountersink 68. For example, bone screw 36 may articulate conically at asolid angle alpha of about thirty degrees.

In operation, sigmoid notch implant 30 articulates with ulnar headimplant 38 to restore stability and pain free natural motion to thedistal radial ulnar joint. To implant sigmoid notch implant 30 thesurgeon first exposes the distal radial ulnar joint. In this discussionof the implantation of sigmoid notch implant 30 it will be assumed thatan ulnar head implant 38 having a metallic articular surface has alreadybeen implanted to replace the head of the ulna. It is specificallycontemplated that sigmoid notch implant 30 may also be implanted toarticulate with the natural head of the ulna as a hemiarthroplasty. Ifthis aspect of the invention is practiced it is to be understood thatsaddle 34 may be formed of a metallic material or another biocompatiblematerial appropriate to articulate with living bone. At this time, it isgenerally thought that for two surface arthroplasty a metal to polymerinterface is preferred and for hemiarthroplasty a metallic to boneinterface is preferred but these beliefs should not be considered to belimiting.

Once the joint is exposed the surgeon removes the head portion 40 of theulnar head implant 38 and sets it aside. First however, the surgeonmeasures from the distal face of the existing ulnar head implant 38 todetermine the location for drilling a hole to accept the stem 44 ofradius portion 32. The surgeon should estimate the drilled depthrequired to accept stem 44. The surgeon then drills a hole in the distalradius utilizing, for example, a 3.5-millimeter drill.

Once the hole to receive stem 44 is drilled the surgeon will use a trialradius portion (not shown) which has an undersized trial stem topreserve a press fit for the sigmoid notch implant 30. Once the trialimplant is satisfactorily placed in the drilled hole the surgeon drillsa pilot hole for the self-tapping bone screw 36 using an appropriatelysized drill. The pilot hole is located so that the pilot hole issubstantially centered in screw hole 58. The pilot hole may be angledfor optimal placement of bone screw 35. The pilot hole may be angled asneeded to avoid pre-existing implant hardware, or to assist in fracturefixation or to avoid fractured portions of the bone. If the pilot holeis drilled non-parallel to the hole to receive stem 44 axial pulloutstrength is increased.

Once the pilot hole for bone screw 36 is made, the surgeon removed thetrial radius portion and burrs down the sigmoid notch to provide a flatbuttress for saddle plate 46. The surgeon also burrs a small countersinkto receive collar 70 and a space to receive stiffening rib 76.

The surgeon places radius portion 32 of sigmoid notch implant 30 so thatstem 44 is in the drilled hole. The surgeon then impacts radius portion32 until it is secured by press fit in the predrilled hole by stem 44and flush against the flat buttress surface of the radius. If the holeis too small to receive stem 44, the surgeon should consider removingradius portion 32 and redrilling to remove debris rather than applyingexcessive force to radius portion 32 in an effort to insert it.

Once radius portion 32 is in place, bone screw 36 is inserted andtightened. It is important that bone screw 36 be tightened evenly andthat saddle plate 46 be evenly supported against the radius to avoidbending saddle plate 46. In addition, care should be taken to protectthe polished surfaces of the ulnar head implant 38 and the radiusportion 32 (for example by handling head portion 40 carefully). Anyscratches on the polished surfaces of the ulnar head implant 38 maydecrease the wear life of saddle 34. Scratches on portions of thecomponents that articulate with surrounding tissues may encourageinflammation.

Referring to FIGS. 18 and 19, the surgeon slides saddle 34 (of UHMWPE orother polymer material) into radius portion 32 so that tongue 100 andgroove 102 mate with groove 62 and ridge 60. When the saddle 34 is about75 percent engaged sloped portion 96 of saddle 34 will engage bevel 66of retaining ridge 56. If need be, the surgeon can stake an osteotomeinto the radius and pry against saddle 34 to overcome the resistance ofretaining ridge 56 against sloped portion 108. Once saddle 34 snaps intoplace in saddle retainer 54 implantation of the sigmoid notch implant 30is complete.

The surgeon then replaces the head portion 40 of ulnar head implant 38and reduces the joint to assess range of motion. Assuming that range ofmotion and alignment is acceptable, the surgeon repairs the jointcapsule and closes the skin.

If the invention is practiced as a hemiarthroplasty, saddle may beformed of metallic material and be secured to radius portion 32 byanother technique as discussed above. In a hemiarthroplasty, the head ofthe ulna will, of course remain intact.

The present invention may be embodied in other specific forms withoutdeparting from the central attributes thereof, therefore, theillustrated embodiments should be considered in all respects asillustrative and not restrictive, reference being made to the appendedclaims rather than the foregoing description to indicate the scope ofthe invention.

1. An orthopedic prosthesis for implantation at the distal radioulnarjoint, the prosthesis comprising: a radius portion adapted to besecurable to the distal radius in the vicinity of the sigmoid fossa; anda saddle including an ulnar facing articular face, the articular facehaving a partially concave, partially convex surface capable ofarticulating with the ulna or a prosthesis that has replaced a head ofthe ulna, the saddle being mechanically securable to the radius portion.2. The prosthesis as claimed in claim 1, in which the radius portioncomprises a plate and a stem, the stem extending outwardly from theplate.
 3. The prosthesis as claimed in claim 1, in which the radiusportion comprises a plate and a saddle retainer to secure the saddle tothe radius portion.
 4. The prosthesis as claimed in claim 1, furthercomprising a bone screw that is articulable with the radius portion tobe angularly adjustable relative to the radius portion.
 5. Theprosthesis as claimed in claim 1, in which the saddle is formed of apolymer and the saddle is shaped to conform to an ulnar head implantthat has replaced the natural ulnar head.
 6. The prosthesis as claimedin claim 2, in which the plate is substantially trapezoidal in shape. 7.The prosthesis as claimed in claim 2, in which the plate comprises asaddle retainer portion located at a perimeter of the plate andsurrounding at least a portion of three sides of the plate.
 8. Theprosthesis as claimed in claim 1, in which the radius portion presents ascrew hole therethrough.
 9. The prosthesis as claimed in claim 8,further comprising a collar surrounding the screw hole.
 10. Theprosthesis as claimed in claim 9, further comprising a stem extendingoutwardly from the plate and a stiffening rib extending from the stem tothe collar.
 11. The prosthesis as claimed in claim 1, in which the ulnarfacing surface comprises a convex portion.
 12. The prosthesis as claimedin claim 1, in which the ulnar facing surface comprises a slopedportion.
 13. The prosthesis as claimed in claim 1, in which the saddleis secured to the radius portion by a tongue and groove interface. 14.The prosthesis as claimed in claim 1, in which at least a portion of theprosthesis expected to be in contact with bone is roughened to encourageosseointegration.
 15. The prosthesis as claimed in claim 1, in which atleast a portion of the prosthesis is titanium plasma coated.
 16. Anorthopedic prosthesis for implantation at the distal radioulnar joint,the prosthesis comprising: a radius portion securable to the distalradius in the vicinity of the sigmoid fossa, the radius portioncomprising a plate and a stem, the stem extending outwardly from a firstside of the plate, the plate further presenting a screw hole; and asaddle attachable to a second side of the plate, the saddle presentingpartially concave partially convex, articular face contoured tocomplement the shape of an ulnar head implant or a natural ulnar head.17. The prosthesis as claimed in claim 17, in which the radius portionfurther comprises a saddle retainer capable of securing the saddle tothe radius portion.
 18. The prosthesis as claimed in claim 17, furthercomprising a bone screw.
 19. The prosthesis as claimed in claim 17,further comprising a spheroidal head bone screw articulable with thescrew hole to be angularly adjustable relative to the plate.
 20. Theprosthesis as claimed in claim 17, in which the plate is substantiallytrapezoidal in shape.
 21. The prosthesis as claimed in claim 17, inwhich the radius portion comprises a saddle retainer portion located atthe perimeter of the plate surrounding at least a portion of three sidesof the plate.
 22. The prosthesis as claimed in claim 17, furthercomprising a collar surrounding the screw hole.
 23. The prosthesis asclaimed in claim 17, further comprising a stem extending outwardly fromthe radius portion and a stiffening rib extending from the stem to thecollar.
 24. The prosthesis as claimed in claim 17, in which thearticular face presents a convex portion.
 25. The prosthesis as claimedin claim 17, in which the articular face presents a sloped portion. 26.The prosthesis as claimed in claim 17, in which the saddle is secured tothe radius portion by a tongue and groove interface.
 27. The prosthesisas claimed in claim 17, in which at least a portion of the prosthesis isroughened to encourage osseointegration.
 28. The prosthesis as claimedin claim 17, in which at least a portion of the prosthesis is titaniumplasma coated.
 29. A method of resurfacing a sigmoid notch of a radiusof a distal radioulnarjoint (DRUJ), the DRUJ including a head of an ulnathe method comprising the steps of: exposing the DRUJ; sculpting theradius in the vicinity of the sigmoid notch to conform to a shape of aradius portion of an implant securing the radius portion of an implantto the radius; attaching a saddle to the radius portion, the saddlehaving an ulnar facing articular face, the articular face having apartially concave, partially convex surface capable of articulating withthe ulna or a prosthesis that has replaced a head of the ulna; andclosing a wound created by exposing the DRUJ.
 30. The method as claimedin claim 30, further comprising the steps of: resecting a head of theulna; and replacing the resected head of the ulna with an ulnar headprosthesis.
 31. The method as claimed in claim 30, further comprisingthe step of drilling a hole in the radius, the hole being sized toreceive a stem that forms a part of the radius portion.
 32. The methodas claimed in claim 30, further comprising the step of drilling a pilothole in the radius to receive a bone screw.
 33. The method as claimed inclaim 33, further comprising the step of inserting a bone screw tlhrougha hole in the radius portion and into the pilot hole; and tightening thebone screw into the pilot hole to secure the radius portion to theradius.
 34. The method as claimed in claim 30, further comprising thestep of engaging a first tongue and groove portion of the saddle with amating second tongue and groove portion of the radius portion.
 35. Themethod as claimed in claim 30, further comprising the step of rougheningat least a portion of a surface of the radius portion to encourageosseointegration.
 36. The method as claimed in claim 36, furthercomprising the step of applying a titanium plasma coating to roughen thesurface.
 37. An orthopedic prosthesis for implantation at the distalradioulnar joint, the prosthesis comprising: means for securing theprosthesis to the distal radius in the vicinity of a sigmoid fossa;means for articulating with a head of the ulna or with an ulnar headimplant that has replaced the resected head of the ulna; and means forretaining the articulating means to the securing means.
 38. Theprosthesis as claimed in claim 38, in which the securing means furthercomprises means for entering the bone of the radius to mechanicallyconnect the prosthesis to the bone.
 39. The prosthesis as claimed inclaim 38, further comprising means for stiffening the securing means.40. The prosthesis as claimed in claim 38, further comprising means forencouraging osseointegration.